Power transducers

ABSTRACT

A transducer arrangement is provided which achieves hard and uniform coupling between the transducer element and the transducer body member by mounting the transducer element in shrink-fit relationship with the body member. Conveniently, to assure uniform pressure on the transducer element, the element is shrink-fitted into an opening provided in the body member.

Hoogenboom 51 Apr. 18, 1972 54-] POWER TRANSDUCERS 3,187,207 6/1965 [72]Inventor: Leo I-loogenboom, Ballston Lake, N.Y.

[73] Assignee: Mechanical Technology Incorporated, 3,390,559 8 Latham,N.Y. 3,339,090 8/1967 Jaffe et al ..310/8.7 X

[22] Filed: Apr. 9, 1970 FOREIGN PATENTS OR APPLICATIONS [21] Appl. No.:26,950 118,239 2/1947 Sweden ..3I0/8.7

52 U.S. Cl ..fiwsizgsgsj ga (1)656 gj -ffig 'jg [5 I 1 Int. Cl. ..I I02k7/00 Anomey joseph v. Claeys and Charles w- Heller [58] Field oISearch..3l0/8.7,9.6,8.8,8.2,8.3, 57 ABSTRACT 517; 308/9, 5, 122' 29/447 5 Atransducer arrangement is provided which achieves hard and uniformcoupling between the transducer element and the 6 I R f d transducerbody member by mounting the transducer element [5 l e erences l e inshrink-fit relationship with the body member. Conveniently, UNITEDSTATES PATENTS to assure uniform prdessure on the transducer element,the element is shrink-fitte into an opening provided in the body3,104,334 9/1963 Bradley et a1 ..310/8.4 member 3,151,258 9/1964Sonderegger.... .....3l0/8.7 3,471,205 10/1969 Farron et al. ..308/9 12Claims, 7 Drawing Figures ,4 :2 5 4/ .50 j/ 4 42 43 4 r a I I 7 43L, lJ44,

POWER TRANSDUCERS This invention relates generally to power transducersand more particularly to new and improved transducer devices and amethod of making such devices. The invention has a wide range ofapplications, only some of which, wherein the invention is especiallyadapted and useful, are described in detail herein. Moreover, in theparticular embodiments of the invention described in detail herein thetransducer elements are of the electrostrictive (piezoelectric) type andare used as mechanical drivers although they may also be used as forcesensors. It is to be understood that the transducer elements may beconstructed of magnetostrictive materials as well. The inventiondescribed herein was made in the performance of work under NASA Contractand is subject to the provisions of Section 305 of the NationalAeronautics and Space Act of 1958, Public Law 85-568 (72 Stat. 435; 42USC 2457).

In recent years ultrasonic energy systems have found wide use in manycommercial and industrial applications such as in cleaning, solderingand in bearings. Briefly, in such systems a transducer element of themagnetostrictive or electrostrictive (piezoelectric) type is driven froma-suitable source of oscillatory energy to produce the desiredvibrations in the transducer element. As is well known, magnetostrictivetransducer elements have the property of changing physical dimensionswhen subjected to an applied magnetic field while electrostrictivetransducer elements have the property of changing physical dimensionswhen subjected to an applied electric field. Conversely when suchelements are subjected to an applied force they have the property ofmodifying the applied field.

Thus, for example, when transducer elements are used as mechanicaldrivers they convert electrical energy to mechanical energy. Theelectrical energy may be supplied, for example, in the form of anoscillating electrical current. The resulting mechanical output is inthe form of repetitive expansions and contractions of the transducer.The frequency of the oscillatory response (forced vibration) of thetransducer corresponds to the frequency of the driving electricaloutput.

When the transducer elements are used as force sensors they convertmechanical force impulses to corresponding electrical impulses which canbe measured by conventional means and a measure of the mechanical forceimposed on the transducer is thus obtained. Calibration of such a deviceto obtain the mechanical force to electrical signal correspondence maybe accomplished in any suitable manner known in the art.

The power generated by power transducers is transmitted to the workingarea by their supporting structure, the design of which will usually bedetermined by the transducer application. Efficient transmission of thepower from the transducer element to the supporting body member, orother supporting structure, requires that hard and uniform coupling beprovided between their interfaces. This is especially true whenultrasonic energy is involved. In addition, many very desirable powertransducer elements are made of crystalline ceramic material, whichmaterials have high compressive strength but low tensile strength.Accordingly, at higher power levels the transducer element must bepreloaded and adequately supported to prevent failure due to internaltensile stresses. Many attempts have been made in the prior art toachieve the required preloading and hard and uniform coupling but nonehave been entirely satisfactory. For example, attempts have been made topreload the elements by clamping arrangements employing external boltsor other fastening means. Such an arrangement has the disadvantage thatconsiderable power dissipation takes place in the bolted joints withsevere local heating. The efficiency of power transfer is thereby muchreduced and the structural failure rate is high.

It is a primary object of the present invention to provide a new andimproved transducer arrangement which overcomes one or more of theforegoing prior art problems and in addition offers a number of distinctadvantages in operation, ease of manufacture, and reliability.

It is another object of the invention to provide a transducerarrangement exhibiting superior transducer element support and givinghigh transmission efficiency between transducer element and supportingstructure.

Another object of the invention is to provide a transducer arrangementexhibiting high reliability and long operating life.

Still another object of this invention is to provide a transducerarrangement wherein the energy density of transmission is high therebymaking possible the use of smaller ceramic crystals and operation atlower voltages.

Yet another object of the invention is a transducer arrangement whichreadily lends itself to the use of mass production techniques withconsequent cost savings.

A still further object of the invention is to provide a new and improvedtransducer arrangement having high dimensional stability permitting thedevice to be used as a mechanical reference, for example, in bearingmetrology.

Briefly stated, in accordance with one aspect of the invention, there isprovided a novel arrangement which achieves both preloading andsupporting of the transducer element or elements in the supportingstructure, or body, as well as hard and uniform coupling thereto. Thenew and improved transducer device comprises the combination of a bodymember and a transducer element in shrink-fit relationship therewith.The transducer element may be constructed by a magnetostrictive materialor an electrostrictive material. Thus, in accordance with an embodimentof the invention a transducer element assembly may be provided whichincludes one or more transducer elements and a transducer elementsupport means associated therewith. The transducer element assembly ismounted and supported in shrink-fit relationship with the supportingbody member. Conveniently, this may beaccomplished by machiningcorresponding internal and external dimensions of the supporting bodymember, transducer elements, and mating transducer elements supportmeans to tolerances of mechanical interference fit; mating surfacesbeing suitably shaped to ensure a hard coupling. If desired thetransducer element may be shrink-fitted to the body member withoututilizing any separate support means. The use of such a support meanshowever allows for a very convenient means of applying an electric fieldacross the element.

The novel features believed characteristic of this invention are setforth with particularity in the appended claims. Theinvention itself,together with its organization and method of operation, as well asadditional objects and advantages thereof, will best be understood fromthe following description taken in conjunction with the accompanyingdrawings, in which:

FIG. 1 is the schematic plan view of a transducer device constructed inaccordance with one embodiment of the inventron;

FIG. 2 is the schematic cross-section of the arrangement shown in FIG. 1taken along the line 2-2 and showing, in addition, attachment ofsuitable electrical connections;

FIG. 3 is a section view showing another embodiment of the invention;

FIG. 4 is a section view showing yet another embodiment of theinvention;

FIG. 4a is a perspective view of the transducer element support memberdisposed between the rectangular transducer elements in FIGS. 3 and 4;

FIG. 5 is a perspective drawing partly in section of the frame of aconical spool bearing incorporating the present invention and FIG. 6 isthe schematic cross-section of the bearing frame in FIG. 5 taken alongthe line 66.

Referring now more particularly to the drawings, there is shown in FIGS.1 and 2 a transducer arrangement in accordance with one embodiment ofthe invention. As shown, the transducer device comprises a transducerelement 11, which may be of a suitable magnetostrictive orelectrostrictive material. As illustrated, element 11 is of hollowcylindrical configuration. To achieve maximum amplitude vibrations whensubjected to an applied field in the radial direction, the material oftransducer element 11 is polarized in the radial direction. A lengthwiseslit 22 is provided in transducer element 11 to prevent the introductionof hoop stresses in the element during assembly or operation. Hoopstresses do not contribute to the generation of power by the transducerelement but rather tend to cause damage to it. Transducer element 11 isshrink-fitted into a supporting body 12 of any desired shape. Element 11has a transducer element support means, shown as a concentric pin 13shrink-fitted into it, as shown. For example, transducer element 11 andpin 13 form a transducer element assembly which is disposed inshrink-fit relationship with the supporting body 12. The supporting body12 and the internal pin 13 may be conveniently used as terminals as wellas supports for the transducer device 10.

As illustrated in FIG. 2, pin 13 may be provided with suitable flexiblemembers which make it possible to attach electrical leads at locationswhere they are not exposed to the adverse effects of high frequencyvibrations. These members can also be used as points of attachment ofexternal supports or suspensions for the transducer device. To this end,annular diaphragms l4 and 15 are provided which terminate in ringsections 16 and 17, respectively. Diaphragms l4 and 15 are formedintegral with the pin 13 and the supporting body 12, respectively. Suchmembers are operative to assure that vibrations of the pin 13 or body 12are not transmitted to the face portions 18 and 19 of the ring sections16 and 17, respectively. Power leads 20 and 21 may be attached to theface portions 18 and -19, as shown in FIG. 2. Oscillatory current maythus be conveniently supplied from a suitable power source (not shown)to the transducer element 11 through leads 20 and 21, annular diaphragms14 and 15, the internal pin 13, and the supporting body 12. Whenoscillatory current is so supplied, the transducer element 11 is setinto a radial or thickness mode of oscillation. The hard and uniformcoupling provided by the novel mounting arrangement of this inventionassures that the mechanical energy so produced is transmitted to thedesired working area of the transducer device.

Any suitable electrostrictive or magnetostrictive material may be usedfor the transducer elements 11. Some examples of materials known toexhibit highly magnetostrictive characteristics are permanickel, nickeland permendur. Especially desirable electrostrictive materials are thepiezoelectric ceramic materials such as lead titanite and leadzirconite. One especially suitable electrostrictive material of thistype is a ceramic material manufactured and sold under the designationPZT4 by the Clevite Corporation. Transducer elements 11 of such materialcan be readily obtained in finish machined form. For some hollowcylindrical transducer elements it is desirable, to assure uniforminternal stresses during operation and allow for operation at lowvoltages, that the thickness of the transducer elements be made smallerthan the radius thereof. For example, in one particular transducerarrangement the transducer thickness was made less than about oneeighthinch. Operation at low power input has the added advantage thatoperating temperatures are lower and any thermally caused frequencydrift is much reduced.

The material of the supporting body 12 is not especially critical,although appropriate physical properties of the transducer element andsupporting body should be properly matched. For example, the materialsfor element 11, pin 13 and body 12 should be selected so that theirmoduli of elasticity are approximately the same. If a transducer elementof PZT4 ceramic material is used, a suitable material for supportingbody 12 and pin 13 would be aluminum or titanium.

The geometric configuration of the supporting body 12 will usually bedetermined by the type and shape of transducer device desired, and thepurpose for which the device is intended. The openings into which thetransducer elements 11 are to be fitted can be machined accurately byconventional means, for example, by boring, broaching or any othersuitable technique. The material of the internal pin 13 may be the sameas that of the supporting body 12. The desired outside finish of pin 13can be obtained in any suitable manner such as, for example, bygrinding. The machining tolerances of all mating surface dimensions aresuch as to provide for a mechanical interference fit. Control of thedegree of shrink-fit is important as this determines the power densitywhich can be transmitted from the transducer element to the supportingbody. Moreover, uneven or excessive loading of the element 11 may damageor depolarize it.

A preferred method of assembly in accordance with another aspect of thisinvention can best be explained by reference to FIGS. 1 and 2. Selectingtransducer element 11 of Clevite PZT4 electrostrictive ceramic materialand the supporting body 12 and internal pin 13 of aluminum, the desiredcompressive preload is achieved with an interference fit of 0.0006 to0.003 inches per linear inch of corresponding component dimension. Thisis conveniently provided by heating the body 12 to a temperature in therange of about 250 to 280 C. The ceramic transducer element 11 is slitaxially to remove and prevent hoop stresses from being developed and thepin 13 is inserted in the central opening thereof. The hollowcylindrical transducer element 11 with the pin 13 therein is cooled toabout 20 C. and disposed in the opening in the heated body 12. When body12 is returned to room temperature the transducer element assembly issupported and mounted in body member 12 and the transducer element 11 isin shrink-fit relationship with such body member and subjected to apreselected compressive loading. In a transducer device constructed asjust described, the preloading of the transducer element 11 may be ofthe order of 2,000 to 10,000 psi. The critical maximum temperature towhich the transducer element may be exposed is the Curie point of thematerial at which temperature the element depolarizes. The Curie pointof Clevite PZT4 ceramic material, for example, is about 325 C. and thehighest compressive load to which it should be sub jected is about10,000 psi.

One criterion by which suitable design and machining tolerances ofcomponents and the correct assembly procedure can be assessed is theinternal power loss under normal operating conditions which can betolerated. This can be expressed conveniently as Q, the ratio of (energystored in the transducer element at zero velocity/energy dissipated percycle). The larger Q, the better the design and the higher theconversion efficiency of the device. Thus, for example, a prior artdevice using separate flanged flexures, large ceramic elements andclamping bolts was considered excellent with Q equal to about 300. Onthe other hand, the Q ofa device in accordance with FIG. 5 ofthisinvention is about 2,500.

Other embodiments of the invention are illustrated in FIGS. 3 and 4. Thebasic concept involved in the arrangements illustrated in FIGS. 3 and 4is the same as that already described. That is, the arrangementcomprises a transducer element shrink-fitted to the body member. In theparticular embodiments illustrated in FIGS. 3 and 4 the arrangementcomprises a transducer element assembly including a transducer elementand a transducer element support means. In these embodiments, however,the transducer element assembly comprises a pair of rectangulartransducer element members with a sheet material member disposedtherebetween. This assembly is then suitably shrink-fitted in a suitablecylindrical opening provided in the supporting body member. Since thetransducer element assembly is of a rectangular configuration, asuitable insert means is provided to achieve a cylindrical surface whichis convenient and effective in obtaining the required shrink-fitrelationship. The insert also assures a pressure uniformity whichotherwise may be difficult to obtain.

In the embodiments shown in FIGS. 3 and 4, therefore, transducerelements 31 and 32 are shaped in the form of short rectangularparallelpipeds. The transducer element support means is in the form of ametallic sheet member 33 located between elements 31 and 32. Thus, sheetmember 33 provides an internal support, an external suspension point ifneeded, and serves also as one of the electrodes. An insert means isprovided to achieve the desired shrink-fit relationship. As shown inFIG. 3, the arrangement includes an insert means 34 of U-shaped crosssection. In the arrangement of FIG. 4, on the other hand, the insertmeans includes two cylindrical segments 35 and 36. The assemblies oftransducer elements, sheet support members, and insert means areshrink-fitted into the body 37 of the device inthe manner previouslydescribed in detail in connection with the embodiment of FIG. 1.Although not shown in FIGS. 3 and 4, electrical connections may also beprovided in the manner already described.

FIG. 5 illustrates the housing of a gaseous squeeze-film bearingincorporating the present invention. As is known in the art, in gaseoussqueeze-film bearings one of the confronting bearing surfaces is made toundergo transverse oscillatory motion. Because of the viscous action andthe non-linear nature of the squeeze motion, the pressure in the gasfilm is higher than ambient and a net load carrying capacity of thebearing is developed.

As shown in FIGS. 5 and 6, transducer elements 41 are of hollowcylindrical configuration. If such transducer elements are made ofelectrostrictive ceramic type material, the crystal structure of theelements is so oriented that their normal mode of oscillation is in theradial direction. Asshown, elements 41 are symmetrically located withinappropriate openings in a supporting body 42. The supporting body 42,which may be of aluminum for example, terminates at each end in suitablyshaped end pieces 43 and 44. The end pieces 43 and 44 of this bearingare shown as being of conical shape, adapted to cooperate withconfronting bearing surfaces of members 43 and 44 although they may beof any other suitable shape consistent with the bearing geometry desiredand the particular bearing application. For example, end pieces 43 and44 would have a spherical shape if a spherical bearing geometry wereused. The end pieces are connected with the central portion of body 42through the weakened sections 45 and 46, shown provided by the grooves47 and 48.

The supporting body 42 is provided with six radial holes in its centerplane, as shown in FIG. 6, into which the tubular ceramic transducerelements 41 are disposed. The tubular ceramic transducer elements 41 areslit axially to eliminate any hoop stresses during assembly andoperation. Each transducer element 41 has a central opening 49 intowhich a suitable solid metal post 50, which may also be of aluminum, isshrink-fitted.

With the foregoing described arrangement the solid center posts 50 serveboth as a convenient mounting means for the bearing assembly as well asone of the electrodes therefor. The outer end of the posts 50 mayterminate in the integral annular diaphragm 51. An electrical connectioncan be conveniently made to the ring portion 52. The external suspensionfor the bearing may also be made to annular diaphragm 51.

In operation, the radial mode of oscillation of the transducer elements41 imparts an axial mode of vibration to the central portion of thesupporting body 42, which vibration is then transmitted to the endpieces 43 and 44 through the weakened sections 45 and 46. The weakenedsections 45 and 46 function as acoustic horns whereby the axialexcursions of the body 42 are magnified at the end pieces 43 and 44.

Another important feature of the present invention is that thedimensional stability of the transducer elements 41 does not affect thebearing gaps. Also, by making the thickness of the transducer elements41 much smaller than the radius thereof, there is no appreciable effecton their. shrink-fit due to dimensional changes during operation atlarger power densities.

The number of transducer elements employed and the location of suchelements in the supporting body is determined by the method of loadingand the performance characteristics of the transducer device sought. Inthe squeeze-film bearing embodiment, uniform motion is required.Consequently the transducer element should be symmetrically disposedabout the periphery of the supporting body. Also, by such a dispositionboth feedback and vibration mode selectivity are achieved. With only onetransducer element, mode control would be much more difficult.

In FIG. 6, the supporting body 42 is illustrated as having six holes,only three of which are shown to be provided with transducer elementassemblies comprising tubular transducer elements 41 and center posts50. In a particular bearing-constructed in accordance with thisembodiment of the invention, satisfactory operation was obtained withtransducer elements mounted in all six holes. Similarly, satisfactorybut different operation was obtained with only three transducer elementsarranged in the symmetric array illustrated in FIG. 6, that is, disposedapart. In both cases, resonant modes were found to exist at 11 Khz and18 Khz. With the'embodiment employing only three transducer elements 41,however, one additional resonant mode was found to be present at about27 Khz. It was found also that this 27 Khz. mode was very powerful andhad a maximum axial amplitude at the cone tip of about 600 microinchesfor a thickness excursion of the transducer element 41 of less than 3microinches.

While there has been described what are considered to be the preferredembodiments of the invention, it will be obvious to those skilled in theart that various changes and modifications may be made therein withoutdeparting from the invention and it is therefore, aimed in the appendedclaims to cover all such changes and modifications as fall within thetrue spirit and scope of the invention.

What we claim as new and desire to secure by United States LettersPatent is:

1. In combination:

a. a body member having an opening therein;

b. a transducer element assembly disposed within said opening in saidbody member and including a hollow cylindrical transducer elementconstructed of a material selected from the group consisting ofelectrostrictive and magnetostrictive materials and a cylindricaltransducer element support member disposed in the interior transducerelement and said transducer element support member being selected toexhibit similar moduli of elasticity and each being dimensioned toeffect a broad area interference fit with each other in the range ofabout 0.0006 to 0.003 inches per linear inch and each of said bodymember and said transducer element support member including an integralannular diaphragm portion adapted to receive an electrical connection.

2. The combination recited in claim 1 wherein said transducer element isconstructed of an electrostrictive material.

3. In combination:

a. a transducer element assembly including a pair of rectangulartransducer elements constructed of a material selected from the groupconsisting of electrostrictive and magnetostrictive materials and arectangular metallic support member thinner and no larger than saidtransducer elements disposed between broad surfaces of each of saidtransducer elements;

b. a metallic body member having at least one opening therein, said bodymember, transducer element and transducer element support member beingselected to exhibit similar moduli of elasticity and each of said bodymember and said transducer element support members including an integralannular diaphragm portion adapted to receive electrical connections; and

. means for mounting and supporting said transducer element and saidtransducer element support member in stress producing relationshipwithin an opening in said body member so that said transducer elementsare subjected to a desired compressive loading.

4. The combination recited in claim 3 wherein said transducer element,said transducer element support means and the opening in said bodymember are dimensioned to effect a broad area interference fit with eachother in the range of about 0.0006 to 0.003 inches per linear inch.

5. The combination recited in claim 4 wherein said transducer element isconstructed of an electrostrictive material.

6. The combination recited in claim 4 wherein said transducer element issubjected to a compressive loading in the order of 2,000 to 10,000 psi.

7. In combination:

a. a body member defining a bearing housing having a radial opening inthe periphery thereof and' a bearing surface adapted for cooperationwith a relatively moveable confronting bearing surface;

b. a transducer assembly including a hollow cylindrical transducerelement constructed of an electrostrictive material and a cylindricaltransducer element support member disposed in the interior centeropening of said hollow cylindrical transducer element, said body member,said transducer element and said transducer element support member beingselected to exhibit similar moduli of elasticity and said transducerelement assembly being disposed within the radial opening of saidbearing housing so that said body member, said transducer element andsaid transducer element support means are in stress producingrelationship with each other operative to subject said transducerelement to a desired compressive loading;

c. means for supplying an oscillatory electric current to saidtransducer element to cause vibrations thereof which vibrations aretransmitted to the bearing surface of said bearing housing. 8. Thecombination recited in claim 7 wherein the bearing housing defined bysaid body member includes a hollow cylindrical central portionterminating at each end in a portion 8 defining a bearing surface,

each of said end portions being connected with the central portionthrough a yieldable portion which is operative to magnify the vibrationstransmitted to the body member from said transducer element.

9. The combination recited in claim 7 wherein said body member defines abearing housing having a plurality of radial openings in the peripherythereof selected ones of which have transducer element assembliesdisposed therein.

10. The combination recited in claim 9 wherein transducer elementassemblies are disposed in radial openings spaced apart.

11. The combination recited in claim 7 wherein said body member and saidtransducer element support means each include integral annular diaphragmmeans which terminate in ring sections adapted to receive electricalconnections for supplying said oscillatory electric current to saidtransducer element.

12. The combination recited in claim 11 wherein said body member definesa bearing housing having a plurality of radial openings in the peripherythereof and transducer element assemblies are disposed in openingsspaced 120 apart.

3,657,581 Dated April 18, 1972 Leo Hoogenboom Patent No.

Inventor(s) It is certified that error appears in the above-identifiedpatent and that said Letters Patent are hereby corrected as' shownbelow: 1

' Column 6, line 31; after "interior" insert center opening. of saidhollow cylindricaltransducer elemenmeaid body member, said Signed andsealed this 12th day of December 1972.

(SEAL) Attest:

EDWARD M.FLETCHER,JR. ROBERT GOTTSCHALK Atteeting Officer I ICommissioner of Patents FORM PC4050 USCOMM-DC 60376-P69 U.$. GOVERNMENTPRINTlNG OFFICE I [99 0-368-31,

1. In combination: a. a body member having an opening therein; b. atransducer element assembly disposed within said opening in said bodymember and including a hollow cylindrical transducer element constructedof a material selected from the group consisting of electrostrictive andmagnetostrictive materials and a cylindrical transducer element supportmember disposed in the interior transducer element and said transducerelement support member being selected to exhibit similar moduli ofelasticity and each being dimensioned to effect a broad areainterference fit with each other in the range of about 0.0006 to 0.003inches per linear inch and each of said body member and said transducerelement support member including an integral annular diaphragm portionadapted to receive an electrical connection.
 2. The combination recitedin claim 1 wherein said transducer element is constructed of anelectrostrictive material.
 3. In combination: a. a transducer elementassembly including a pair of rectangular transducer elements constructedof a material selected from the group consisting of electrostrictive andmagnetostrictive materials and a rectangular metallic support memberthinner and no larger than said transducer elements disposed betweenbroad surfaces of each of said transducer elements; b. a metallic bodymember having at least one opening therein, said body member, transducerelement and transducer element support member being selected to exhibitsimilar moduli of elasticity and each of said body member and saidtransducer element support members including an integral annulardiaphragm portion adapted to receive electrical connections; and c.means for mounting and supporting said transducer element and saidtransducer element support member in stress producing relationshipwithin an opening in said body member so that said transducer elementsare subjected to a desired compressive loading.
 4. The combinationrecited in claim 3 wherein said transducer element, said transducerelement support means and the opening in said body member aredimensioned to effect a broad area interference fit with each other inthe range of about 0.0006 to 0.003 inches per linear inch.
 5. Thecombination recited in claim 4 wherein said transducer element isconstructed of an electrostrictive material.
 6. The combination recitedin claim 4 wherein said transducer element is subjected to a compressiveloading in the order of 2, 000 to 10,000 psi.
 7. In combination: a. abody member defining a bearing housing having a radial opening in theperiphery thereof and a bearing surface adapted for cooperation with arelatively moveable confronting bearing surface; b. a transducerassembly including a hollow cylindrical transducer element constructedof an electrostrictive material and a cylindrical transducer elementsupport member disposed in the interior center opening of said hollowcylindrical transducer element, said body member, said transducerelement and said transducer element support member being selected toexhibit similar moduli of elasticity and said transducer elementassembly being disposed within the radial opening of said bearinghousing so that said body member, said transducer element and saidtransducer element support means are in stress producing relationshipwith each other operative to subject said transducer element to adesired compressive loading; c. means for supplying an oscillatoryelectric current to said transducer element to cause vibrations thereofwhich vibrations are transmitted to the bearing surface of said bearinghousing.
 8. The combination recited in claim 7 wherein the bearinghousing defined by said body member includes a hollow cylindricalcentral portion terminating at each end in a portion defining a bearingsurface, each of said end portions being connected with the centralportion through a Yieldable portion which is operative to magnify thevibrations transmitted to the body member from said transducer element.9. The combination recited in claim 7 wherein said body member defines abearing housing having a plurality of radial openings in the peripherythereof selected ones of which have transducer element assembliesdisposed therein.
 10. The combination recited in claim 9 whereintransducer element assemblies are disposed in radial openings spaced120* apart.
 11. The combination recited in claim 7 wherein said bodymember and said transducer element support means each include integralannular diaphragm means which terminate in ring sections adapted toreceive electrical connections for supplying said oscillatory electriccurrent to said transducer element.
 12. The combination recited in claim11 wherein said body member defines a bearing housing having a pluralityof radial openings in the periphery thereof and transducer elementassemblies are disposed in openings spaced 120* apart.